Adhesion ~ the attraction between two atoms and
molecules at the contacting surfaces of different
materials; it can be chemical (ionic), physical (van der
Waals’), and/or mechanical (micro- or macrointerlocking)
Adhesive ~ monomer (or related) that penetrates and
establishes intimate contact with the conditioned tissue
substrate, polymerises, and forms a strong bond
between such substrate and the restorative material
Priming ~ cleaning, structural alteration, and
increasing adhesiveness of the substrate.
Etching ~ dissolution of the substrate, removed by
rinsing to enhance intimate contact of adhesives
Wetting ~ the ability of a liquid to come into
intimate contact with solid substrate; facilitates
Human dentin is a heterogenous material composed
of a solid (circumpulpal) phase surrounding a
network of tubules.
These tubules, measuring about 1 to 3 micrometer in
diameter, contain elongated cell bodies that radiate
from the the dental pulp organ throughout the entire
Their average density is about 30 000 tubules/square
Structurally dentin is
composed of mineral
crystals deposited between a
network of protein fibrils.
Approximately 90% of this
network is type I collagen,
the balance consisting of a
sheath of phosphoproteins
surrounding the collagen,
and other proteins in small
% by volume
Low surface free
energy - wets less
Complex histologic structure and variable composition of
Whereas enamel is 92% inorganic hydroxyapatite by
volume, dentine is (on average) only 45% inorganic.
Also dentinal hydroxyapatite is randomly arranged in an
organic matrix that consists primarily of collagen, which
is permeated throughout by tubules.
These contain vital processes of the pulp odontoblasts.
Hence, vital dentine is a sensitive structure.
The high water content provides competition with any
adhesive biomaterial for bonding to dentine.
Tooth surface instrumented with a rotary or manual
To achieve a strong bond, it is necessary to either
strengthen this smear-layer in situ or to remove it
In the latter, it is imperative to ensure an adequately
adhesive restorative otherwise the open tubules may
allow irritants or bacteria greater access to the pulp.
Removes smear layer.
Exposes a microporous scaffold of collagen fibrils
increasing the microporosity of intertubular dentin.
Various acids used
Three categories of dentinal adhesives are proposed:
Category I includes adhesives with shear bond
strength values between 5 and 7 Mpa;
Category II includes dentinal adhesives with shear
bond strengths between 8 and 14 Mpa; and
Category III includes adhesives with shear bond
strength values above 20 Mpa .
2.9 to 7.1% by volume
17-20 MPa bond strength to overcome (Davidson et al)
According to generations:
No etch to
These contained N-phenylglycine and glycidyl
methacrylate or NPG-GMA.
NPG-GMA is a bifunctional molecule or coupling
This means that one end of this molecule bonds to
dentin while the other bonds (polymerizes) to
The bond strengths of these early systems were only
1 to 3 MPa.
In the late1970s, the second-generation systems
The majority of these incorporated halophosphorous
esters of unfilled resins such as bisphenol- A
glycidyl methacrylate, or bis-GMA, or hydroxyethyl
methacrylate, or HEMA.
The mechanism by which these bonded to dentin
were postulated to be through an ionic bond to
calcium by chlorophosphate groups.
These were weak bonds with a range of 2-7 MPa.
Since dentin was not etched in these early bonding
systems bonding was with the smear layer.
Three step systems.
Dentin etching was introduced by Fusuyama.
Followed by a primer application.
Application of an unfilled resin.
The primer contains hydrophilic resin monomers
which include hydroxyethyl trimellitate anhydride,
or 4-META, and biphenyl dimethacrylate, or
The primers contain a hydrophilic group that
infiltrates the smear layer, modifying it and
promoting adhesion to dentin, and the hydrophobic
group of the primer creates adhesion to the resin.
Dentin primers may be 6 % phosphate pentaacrylate, (PENTA) ; 30 % HEMA; and 64 %
Fusayama and colleagues tried to simplify bonding to
enamel and dentin by total etching the preparation with 40
percent phosphoric acid.
The mineralized tissues of the peritubular and intertubular
dentin are dissolved by the acidic action; the initial surface
penetration exposes the collagen fibers.
In this area, for a depth of 2 to 4 micrometers, hybridization
takes place, and resin tags can seal the tubule orifices firmly .
Results from the polymerized methacrylate and
The hybrid layer is defined as “the structure formed
in dental hard tissues (enamel, dentin, cementum)
by demineralization of the surface and subsurface,
followed by infiltration of monomers and
Nakabayashi et al (1982)
The formation of resin tags and adhesive lateral
branches complete the bonding mechanism between
the adhesive material and etched dentin substrate.
All Bond 2
Liner Bond 2
Unique feature is the combination of the priming
and bond resin application steps, resulting in a one
Also rely heavily on wet bonding.
Most commonly used and probably the most
These bonding systems create a mechanical
interlocking with etched dentin by means of resin
tags, adhesive lateral branches and hybrid layer
3 step total etch
Gluma Comfort Bond
Adper Single Bond
Prime & Bond- NT
Mean Shear Bond Strength
( MPa )
Opti Bond Solo
Prime & Bond 2.1
They are self etching adhesives ( Etch & prime
They involve a somewhat different mechanism in
that, as soon as the decalcification process is
initiated, the infusion of the evacuated spaces by
dentin bonding agent is begun.
As a result, the potential for residual vacancies
amongst the collagenous fibers is dramatically
reduced or eliminated altogether.
The bonding agent is either applied after the self
etching primer or mixed together before single
All in one
Clearfil SE Bond
Prompt L Pop
All in one
Modify the smear layer & incorporate it into the
One step – Prime & Bond 2.1
Two step – Pro Bond
2. Completely removes the smear layer:
Two step – Clearfil Liner Bond 2.
Three step – Clearfil Liner Bond.
3. Dissolves the smear layer than removing it.
Prime & Bond 2.0.
Difference in the degree of mineralisation.
Concentrations of both calcium and phosphorus in
both peritubular and intertubular dentin are lower in
The tubular diameter and density in dentin of
primary teeth is lesser than that in permanent teeth.
Dentin of primary teeth is more sensitive to the acid
etch/ conditioning procedure.
This leads to an increased thickness of the hybrid
layer and the subsequent lack of complete
penetration of the adhesive resin into the
Ideally the concentration and duration of etch/
conditioning has to be re-calculated for primary
Carious dentin is a combination of porous and nonporous zones.
The resultant deposition of Whitlockite may warrant
additional etching/ conditioning times compared to
Simple to use.
Minimally irritating to the tissue.
Less technique sensitive.
Clinically satisfactory bond.
Chemically bonding the resin molecule to the
collagenous structure of dentin rather than by means
of micromechanical retention (as is done now).
Incidentally, another approach to dentinal adhesion
could center on the chemical bonding of the resin to
the hydroxyapatite .
Prime & Bond 2.0 – Total etch
Prime & Bond 2.1 – No etch
Prime & Bond NT – Nano-Technology
Drying the dentin will produce a relatively
impermeable amorphous layer:
Collapse of collagen layer
Must remain moist to resist this impermeable layer.
Pooled moisture should be removed by blotting and
not with a blast of air.
Dry dentin should be remoistened with a wet cotton
The total-etch technique permits the etching of
enamel and dentin simultaneously using phosphoric
acid for 15 to 20 seconds.
The surface must be left moist (“wet bonding”),
however, in order to avoid collagen collapse .
The application of a hydrophilic primer solution
infiltrates the exposed collagen network forming the
hybrid layer .
Smear layer not removed in second
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